They are the space probes that will not quit. Many of us are looking to retire after more than 30 years of work. Not NASA's two Voyager spacecraft, racing through interstellar space. VOA's Paul Sisco has more.

Late summer 1977: Voyagers 1 and 2 rocketed into space within weeks of each other from their Florida launch pad.

They were built to last five years and make close-up observations of the planets Jupiter and Saturn and their larger moons. With "mission accomplished" and energy to spare, in 1982 they flew to Uranus and Neptune, the two outermost giants in the solar System.

Project scientist Ed Stone remembers. "As a scientist it was just an incredible period of discovery, and even today, as we head to interstellar space, we're still discovering things we had not thought about before. But as we flew by Jupiter and then Saturn and then Uranus and Neptune we discovered world after world which had just been points of light and each was distinct and different."

On Jupiter's moon, Io, the Voyager mission discovered the first active volcanoes ever seen beyond Earth. Next, they gave us fascinating detail of Saturn's rotating rings and unexpected dark areas.

As the probes passed each body, they were flung deeper into space.

With images and data of Uranus's moon, Miranda, NASA scientists created a three dimensional animation of its rugged surface and bizarre canyons more that 25 kilometers deep.

Voyagers taught us that Neptune has the fastest winds of any planet, up to 2,000 kilometers per hour.

"Voyager is the little space craft that could," says Roger Launius, who is a space historian at the Smithsonian's National Air and Space Museum in Washington, DC. "And Voyager is out there. It is beyond the point where the solar system has any real hold on it any longer from a gravitational perspective."

The crafts are running out of power quickly, but will still send bits of information back to Earth for at least a few more years. The Voyagers also carry two gold-plated discs [phonograph records, the audio technology of the time], should there ever be a chance encounter from a distant world. The greeting says, "Hello from the children of planet Earth ..."

Launius explains, "These gold records have greetings in 76 languages. They have snippets of music and poetry and photographs and things of that nature to talk about what life on Earth is like.

The messages are intended to let those who find them know that we exist.